In general, gasoline or gas oil is used in an internal-combustion engine of a car. Such a fuel is a mixture of various hydrocarbons and other materials. In the light of concerns about a future reduction in the output of fossil fuels and in the light of a strong request for a reduction in emission of carbon dioxide in the fight against global warming, it is currently being studied that alcohol (e.g., ethanol or methanol) which is a plant-derived fuel is mixed in the gasoline for the fuel of an internal-combustion engine.
The material composition of such a fuel is determined based on the material composition and distillation condition of crude oil which is the raw material of gasoline or gas oil, addition amount of alcohol, and the like. Accordingly, properties concerning combustion of such a fuel differ depending on the material composition thereof. Therefore, even if a combustion condition (air-fuel ratio or amount of fuel injection per unit time) on the internal-combustion engine side is optimally set on the assumption of combustion of one fuel having a given material composition, the combustion condition is not optimal for another fuel in some cases.
In order to increase the output efficiency of the internal-combustion engine to reduce fuel consumption and, at the same time, to reduce the amount of hydrocarbon (HC) or carbon monoxide (CO) which is a product of incomplete combustion contained in exhaust gas, air needs to be mixed with a fuel to be supplied to the internal-combustion engine at an ideal ratio (i.e., air-fuel ratio is optimized) for combustion depending on the kind of the fuel.
In order to make the material composition of a fuel constant and thereby prevent the optimal combustion condition from being changed, it is now proposed that one material or a mixture of, at most, two materials selected from hydrocarbons (such as pentane, cyclohexane, octane) which are components of the fossil fuel and alcohols (such as methanol, and ethanol) are used as a fuel. This type of fuel roughly includes a hydrocarbon-based fuel and alcohol-based fuel.
When such various types of fuels are sold in the same manner in service station and the like, it becomes likely that a fuel tank in a car is erroneously replenished with a fuel different from a predetermined one. If such occurs, the engine output efficiency may decrease extremely. Such a situation must be avoided.
Therefore, it is desirable that a car is to be provided with a mechanism capable of detecting the type of a fuel to be supplied from its fuel tank to internal-combustion engine and checking whether the supplied fuel is a predetermined one.
Further, in the case where the detected type of the fuel is similar to a predetermined one, it is desirable to optimize the combustion condition of the internal combustion engine depending on the detected type. That is, it is desirable to identify the type of the fuel to be actually supplied to the internal combustion engine and appropriately set the combustion condition of the internal combustion engine based on the identification result and thereby realize a suitable combustion state (i.e., combustion state that increases the output torque of the internal-combustion engine while reducing the amount of products of incomplete combustion contained in exhaust gas) in accordance with the type of the fuel to be actually used in the combustion.
Since the combustion properties and physical properties of the hydrocarbon-based fuel differ from those of the alcohol-based fuel, it is important to firstly determine a group, i.e. hydrocarbon-based fuel or alcohol-based fuel, to which a liquid (fuel) to be measured belongs. It is preferable, after the determination, to identify in more detail the type of the hydrocarbon-based fuel or that of the alcohol-based fuel.
A method of identifying the type of a fluid including a liquid is disclosed in, e.g., JP-A-11-153561 (Patent Document 1). This method comprises supplying an electric current to a heating body so as to generate heat to thereby heat a temperature-sensitive body, giving thermal effect to the heat transfer from the heating body to temperature-sensitive body using a fluid to be identified, and identifying the type of the fluid to be identified based on an electrical output value corresponding to the impedance of the temperature-sensitive body. In this fluid identification method, a current is periodically supplied to the heating body.
Patent Document 1: JP-A-11-153561 (paragraphs [0042] to [0049])